Android之自定義ContentProvider的實作（Very Very 用心）

剛開始學習ContentProvider時是學的系統的ContentProvider，沒碰到什么問題，但是在學習自定義ContentProvider的實作時，唉，碰到好幾個問題，花了我好多時間，

我碰到的問題：

1. java.lang.IllegalArgumentException: column '_id' does not exist

解決方法：創建資料表時插入一個名為_id的列，型別為自增量，因為在使用Cursor相關的Adapter時需要用到這個列

2.Failed to find provider <authority> for user 0 ; expected to find a valid ContentProvider for

解決方法：在第一個應用的AndroidManifest.xml中添加如下代碼

 <provider
            android:authorities="cn.sch.myprovider"
            android:name=".MyProvide"
            android:exported="true"
            android:multiprocess="false"
            android:grantUriPermissions="true"
            android:writePermission="cn.sch.myprovider.Write"
            android:readPermission="cn.sch.myprovider.Read"
            >
        </provider>

但是當我使用API 30時卻還是會報錯，報空指標例外，到現在還沒解決，真的菜啊，所以為了讓程式運行起來，我就選擇API 29 ，就能正常運行了

3.注意：在資料庫類里寫sql陳述句時，最容易出錯，比如少了空格拼接起來就是錯誤的sql陳述句，英文逗號寫成中文逗號，進行增刪改查時表名，列名要寫正確

4.Uri里的authorities也非常容易搞錯，搞錯了就會報 uri 找不到例外

5.還有很多小問題就不一一描述了，細心認真點，相信你們自己能解決

為了讓你們（新手,包括我自己）能正確的運行起我的程式來，我把所有類，布局檔案和配置資訊都貼出來，如果你去看別人寫的自定義ContentProvider的實作，你會發現有這幾個問題，不敢說全部，大多數是這樣，自定義ContentProvider的實作本來就是面向新手的，所以把資訊都寫全來才好去學習和模仿加創新，

1.缺少布局檔案，對于我這種小白來說真的就離譜，id都不知道哪個是哪個

2.缺少一些類，不如資料庫類，

3.只貼出一些重要代碼片段來，對于小白來說，的確不好搞

4.缺少配置資訊，這只能看看，要想模仿就難了，一大堆BUG等著你

5.完整的原始碼要VIP或者收費

專案里的代碼詳解我就不說了，大多數都有解釋，實在不懂的，可以自行百度，肯定比我在這說的清楚詳細易懂，我這篇給文章主要還是讓各位實作自定義ContentProvider，能跑起來

先來看看我效果

注意：視頻中的洗掉我是按序號洗掉的，比如表中有一條記錄：

序號：1 姓名：小明 作業：Android Development

然后我在輸入框中輸入，只要序號是1，不管姓名和作業輸的是什么，都會將

序號：1 姓名：小明 作業：Android Development 這條記錄洗掉，

（感興趣的可以自己去改改）

首先看一下我的專案結構，你就知道要寫哪些類和布局檔案了

模塊gamedemo是第一個應用

MainActivity代碼如下

import android.app.Activity;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity implements View.OnClickListener {

    private static final String TAG = "lzs";
    private DbHelp dbHelp;
    private SQLiteDatabase db;
    private TextView userTv;
    private Button btn_query;
    private Button btn_insert;
    private Button btn_delete;
    private Button btn_update;
    private int m=2;
    private int n=3;
    private EditText xuhao;
    private EditText xingming;
    private EditText zhiye;
    private int id;
    private String name;
    private String job;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        this.dbHelp = new DbHelp(this); //創建資料庫
        this.db = this.dbHelp.getWritableDatabase();
        init(); //初始化控制元件
    }

    private void init() {
        btn_query = findViewById(R.id.btn_query);
        btn_insert = findViewById(R.id.btn_insert);
        btn_delete = findViewById(R.id.btn_delete);
        btn_update = findViewById(R.id.btn_update);
        xuhao = findViewById(R.id.xuhao);
        xingming = findViewById(R.id.xingming);
        zhiye = findViewById(R.id.zhiye);

        btn_query.setOnClickListener(this);
        btn_insert.setOnClickListener(this);
        btn_delete.setOnClickListener(this);
        btn_update.setOnClickListener(this);
    }

    @Override
    protected void onStart() {
        super.onStart();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        db.close();
        dbHelp.close();
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.btn_query:
                btn_query();
                break;
            case R.id.btn_insert:
                btn_insert();
                break;
            case R.id.btn_delete:
                btn_delete();
                break;
            case R.id.btn_update:
                btn_update();
                break;
        }
    }


    //查詢函式
    private void btn_query(){

        Cursor user = this.db.query("user", null, null, null, null, null, null);
        this.userTv = findViewById(R.id.id_user_db);

        //清空文本，防止重復查詢而多次顯示
        if(!TextUtils.isEmpty(this.userTv.getText()))
        {
            this.userTv.setText("");
        }

        while (user.moveToNext()){
            String id = user.getString(0);
            String name = user.getString(1);
            String jobs = user.getString(2);
            this.userTv.append("序號:"+id+"  姓名:"+name+"  作業:"+jobs+"\n");
        }
    }
    //插入函式(沒有用SQL陳述句，用的是Android的方式)
    private void btn_insert(){
        if(!TextUtils.isEmpty(xuhao.getText())&&!TextUtils.isEmpty(xingming.getText())&&!TextUtils.isEmpty(zhiye.getText())){
            id = Integer.parseInt(xuhao.getText().toString());
            name = xingming.getText().toString();
            job = zhiye.getText().toString();
            Cursor result=db.rawQuery("select * from user where _id = "+id,null);
            if(!result.isAfterLast()){
                Toast.makeText(MainActivity.this,"插入失敗，改記錄已存在或序號重復！",Toast.LENGTH_SHORT).show();
            }else {
                Uri uri_user = Uri.parse("content://cn.sch.myprovider/user");
                // 向user表插入資料
                ContentValues values3 = new ContentValues();
                values3.put("_id", id);
                values3.put("name", name);
                values3.put("jobs", job);
                // 獲取ContentResolver
                ContentResolver resolver3 = getContentResolver();
                // 通過ContentResolver 根據URI 向ContentProvider中插入資料
                resolver3.insert(uri_user, values3);
                Toast.makeText(MainActivity.this,"插入成功",Toast.LENGTH_SHORT).show();
            }

        }else {
            Toast.makeText(MainActivity.this,"請填寫完整，不能為空！",Toast.LENGTH_SHORT).show();
        }
    }
    //洗掉函式(利用SQL陳述句洗掉，你也可以用Android的方式洗掉)，因為序號是唯一的，所以直接根據提供的序號洗掉就可以了
    private void btn_delete(){
        if(!TextUtils.isEmpty(xuhao.getText())){
            id = Integer.parseInt(xuhao.getText().toString());
            Cursor result=db.rawQuery("select _id from user where _id="+id,null);
            if(!result.isAfterLast()){
                db.execSQL("delete from user where _id="+id);
                Toast.makeText(MainActivity.this,"洗掉成功",Toast.LENGTH_SHORT).show();
            }else {
                Toast.makeText(MainActivity.this,"洗掉失敗，沒有該條記錄！",Toast.LENGTH_SHORT).show();
            }

        }else {
            Toast.makeText(MainActivity.this,"請填寫完整，不能為空！",Toast.LENGTH_SHORT).show();
        }

    }
    //更新函式(利用SQL陳述句更新，你也可以用Android的方式更新)，因為序號唯一，所以直接根據輸入的序號更改就可以了
    private void btn_update(){
        if(!TextUtils.isEmpty(xuhao.getText())&&!TextUtils.isEmpty(xingming.getText())&&!TextUtils.isEmpty(zhiye.getText())){
            id = Integer.parseInt(xuhao.getText().toString());
            name = xingming.getText().toString();
            job = zhiye.getText().toString();
            Cursor result=db.rawQuery("select * from user where _id="+id,null);
            if(!result.isAfterLast()){
                db.execSQL("update user set _id="+id +" where _id="+id);
                db.execSQL("update user set name='"+name +"' where _id="+id);//注意是 set='name'  如果不清楚可以再去看看資料庫的知識
                db.execSQL("update user set jobs='"+job +"' where _id="+id);
                Toast.makeText(MainActivity.this,"更新成功",Toast.LENGTH_SHORT).show();
            }else {

                Toast.makeText(MainActivity.this,"更新失敗，改記錄不存在！",Toast.LENGTH_SHORT).show();
            }

        }else {
            Toast.makeText(MainActivity.this,"請填寫完整，不能為空！",Toast.LENGTH_SHORT).show();
        }

    }

}

MainActivity的布局檔案activity_main.xml 代碼如下

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:gravity="center"
        android:orientation="vertical">

        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginBottom="50dp"
            android:text="第一個應用"
            android:textSize="30dp"/>

        <TextView
            android:id="@+id/id_user_db"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginBottom="250dp"
            android:text="" />

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="2"
        android:gravity="center"
        android:orientation="vertical">


        <EditText
            android:id="@+id/xuhao"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:ems="10"
            android:hint="請輸入序號"
            android:inputType="number" />

        <EditText
            android:id="@+id/xingming"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:ems="10"
            android:hint="請輸入姓名"
            android:inputType="textPersonName" />

        <EditText
            android:id="@+id/zhiye"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:ems="10"
            android:hint="請輸入職業"
            android:inputType="textPersonName" />

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="2"
        android:orientation="vertical">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:gravity="center"
            android:orientation="horizontal">

            <Button
                android:id="@+id/btn_query"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="20dp"
                android:text="查詢資料" />

            <Button
                android:id="@+id/btn_insert"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginLeft="20dp"
                android:layout_marginTop="20dp"
                android:text="插入資料" />
        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:gravity="center_horizontal"
            android:orientation="horizontal">

            <Button
                android:id="@+id/btn_delete"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="洗掉資料" />

            <Button
                android:id="@+id/btn_update"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginLeft="20dp"
                android:text="更新資料" />
        </LinearLayout>
    </LinearLayout>

</LinearLayout>

MyProvide代碼如下

import android.content.ContentProvider;
import android.content.ContentValues;
import android.content.Context;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;


public class MyProvide extends ContentProvider {

    private Context mContext;
    private DbHelp dbHelp = null;
    private SQLiteDatabase db = null;

    public static final String AUTHORITY = "cn.sch.myprovider";

    public static final int User_Code = 1;

    private UriMatcher mMatcher;

    @Override
    public boolean onCreate() {
        mContext = getContext();
        mMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        //初始化
        // 若URI資源路徑 = content://cn.sch.myprovider/user ，則回傳注冊碼User_Code
        mMatcher.addURI(AUTHORITY, "user", User_Code);

        dbHelp = new DbHelp(mContext);
        this.db = dbHelp.getWritableDatabase();
        // 初始化表的資料
        db.execSQL("delete from user");
        db.execSQL("insert into user values(1,'xiaoming','Android Development')");
        db.execSQL("insert into user values(2,'xiaohua','Java Development')");
        return true;
    }

    @Override
    public Cursor query( Uri uri,  String[] projection, String selection,  String[] selectionArgs, String sortOrder) {
        String tableName = getTableName(uri);
        return db.query(tableName,projection,selection,selectionArgs,null,null,sortOrder,null);
    }

    @Override
    public String getType( Uri uri) {
        return null;
    }

    @Override
    public Uri insert( Uri uri,  ContentValues values) {
        String tableName = getTableName(uri);
        //向表中插入資料
        db.insert(tableName,null,values);
        mContext.getContentResolver().notifyChange(uri,null);
        return uri;
    }

    @Override
    public int delete( Uri uri,  String selection,  String[] selectionArgs) {
        String tableName = getTableName(uri);
        int count=db.delete(tableName, null, null);
        if(count>0){
            getContext().getContentResolver().notifyChange(uri, null);
            return count;
        }
        return 0;
    }

    @Override
    public int update( Uri uri,  ContentValues values,  String selection,  String[] selectionArgs) {
        String tableName = getTableName(uri);
        int count = db.update(tableName, values, selection,selectionArgs);
        if(count>0){
            getContext().getContentResolver().notifyChange(uri, null);
            return count;
        }
        return 0;
    }


    private String getTableName(Uri uri) {
        String tableName = null;
        switch (mMatcher.match(uri)){
            case User_Code:
                tableName = DbHelp.USER_TABLE_NAME;
                break;
        }
        return tableName;
    }

}

DbHelp代碼如下

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DbHelp extends SQLiteOpenHelper {
    // 資料庫名
    private static final String DATABASE_NAME = "finch.db";
    // 表名
    public static final String USER_TABLE_NAME = "user";
    //資料庫版本號
    private static final int DATABASE_VERSION = 1;

    public DbHelp(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        //創建資料庫表
        //注意;如果你第一次運行后第二次又改動創建資料陳述句時，并且只改動了屬性，沒有該表名，那么當你再次運行App時會發現會報錯，新改動的屬性不存在
        //解決方法：手動將已建好的那個表洗掉，或者洗掉App重新安裝，這樣你改動的屬性才能生效
        db.execSQL("CREATE TABLE IF NOT EXISTS "+USER_TABLE_NAME+"(_id INTEGER PRIMARY KEY AUTOINCREMENT,"+" name TEXT,"+"jobs TEXT)");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}

第一個應用的AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="com.example.gamedemo">

    <uses-permission android:name="android.permission.READ_PERSON_DB" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"
        tools:ignore="ProtectedPermissions" />

    <uses-permission android:name="cn.sch.myprovider.Read"/>
    <uses-permission android:name="cn.sch.myprovider.Write"/>

    <permission android:name="cn.sch.myprovider.Read"
        android:label="Permission for read content provider"
        android:protectionLevel="normal"
        ></permission>

    <permission android:name="cn.sch.myprovider.Write"
        android:label="Permission for write content provider"
        android:protectionLevel="normal"
        ></permission>


    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.MyApplication1">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <provider
            android:authorities="cn.sch.myprovider"
            android:name=".MyProvide"
            android:exported="true"
            android:multiprocess="false"
            android:grantUriPermissions="true"
            android:writePermission="cn.sch.myprovider.Write"
            android:readPermission="cn.sch.myprovider.Read"
            >
        </provider>
    </application>

</manifest>

第一個應用的build.gradle

plugins {
    id 'com.android.application'
}

android {
    compileSdk 29

    defaultConfig {
        applicationId "com.example.gamedemo"
        minSdk 21
        targetSdk 29
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

dependencies {

    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'com.google.android.material:material:1.3.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
}

模塊contentprovidertest是第二個應用

MainActivity代碼如下

package com.example.contentprovidertest;

import android.Manifest;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private static final String TAG = "lzs";
    private TextView userTv;
    private Button btn_query2;
    private Button btn_insert2;
    private Button btn_delete2;
    private Button btn_update2;
    private EditText xuhao2;
    private EditText xingming2;
    private EditText zhiye2;
    private int id;
    private String name;
    private String job;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        this.userTv = findViewById(R.id.id_tv);

        //動態獲取權限
        if(ActivityCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE)==PackageManager.PERMISSION_GRANTED
                ||ActivityCompat.checkSelfPermission
                (this, Manifest.permission.WRITE_EXTERNAL_STORAGE)==PackageManager.PERMISSION_GRANTED) {
            init(); //初始化控制元件
        }else {
            ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.READ_EXTERNAL_STORAGE,Manifest.permission.WRITE_EXTERNAL_STORAGE},0x10);
        }
    }

    private void init() {

        xuhao2 = findViewById(R.id.xuhao2);
        xingming2 = findViewById(R.id.xingming2);
        zhiye2 = findViewById(R.id.zhiye2);

        btn_query2 = findViewById(R.id.btn_query2);
        btn_insert2 = findViewById(R.id.btn_insert2);
        btn_delete2 = findViewById(R.id.btn_delete2);
        btn_update2 = findViewById(R.id.btn_update2);

        btn_query2.setOnClickListener(this);
        btn_insert2.setOnClickListener(this);
        btn_delete2.setOnClickListener(this);
        btn_update2.setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.btn_query2:
                btn_query2();
                break;
            case R.id.btn_insert2:
                btn_insert2();
                break;
            case R.id.btn_delete2:
                btn_delete2();
                break;
            case R.id.btn_update2:
                btn_update2();
                break;
        }
    }

    private void btn_update2() {
        id = Integer.parseInt(xuhao2.getText().toString());
        name = xingming2.getText().toString();
        job = zhiye2.getText().toString();
        if(!TextUtils.isEmpty(xuhao2.getText())&&!TextUtils.isEmpty(xingming2.getText())&&!TextUtils.isEmpty(zhiye2.getText())){
            Uri uri = Uri.parse("content://cn.sch.myprovider/user");
            ContentResolver resolver2 = getContentResolver();
            ContentValues values2 = new ContentValues();
            values2.put("_id", id);
            values2.put("name", name);
            values2.put("jobs", job);
            resolver2.update(uri,values2,"_id="+id,null);
            Toast.makeText(MainActivity.this, "更新成功", Toast.LENGTH_SHORT).show();
        }else {
            Toast.makeText(MainActivity.this,"請填寫完整，不能為空！",Toast.LENGTH_SHORT).show();
        }

    }

    private void btn_delete2() {
        id = Integer.parseInt(xuhao2.getText().toString());
        if(!TextUtils.isEmpty(xuhao2.getText())){
            Uri uri = Uri.parse("content://cn.sch.myprovider/user");
            ContentResolver resolver2 = getContentResolver();
            resolver2.delete(uri,"_id ="+id,null);
            Toast.makeText(MainActivity.this, "洗掉成功", Toast.LENGTH_SHORT).show();
        }else {
            Toast.makeText(MainActivity.this,"請填寫完整，不能為空！",Toast.LENGTH_SHORT).show();
        }

    }

    private void btn_insert2() {

        this.userTv.setText("");
        id = Integer.parseInt(xuhao2.getText().toString());
        name = xingming2.getText().toString();
        job = zhiye2.getText().toString();
        if(!TextUtils.isEmpty(xuhao2.getText())&&!TextUtils.isEmpty(xingming2.getText())&&!TextUtils.isEmpty(zhiye2.getText())){
            Uri uri = Uri.parse("content://cn.sch.myprovider/user");
            // 插入表中資料
            ContentValues values2 = new ContentValues();
            values2.put("_id", id);
            values2.put("name", name);
            values2.put("jobs", job);
            // 獲取ContentResolver
            ContentResolver resolver2 = getContentResolver();
            // 通過ContentResolver 根據URI 向ContentProvider中插入資料
            resolver2.insert(uri, values2);
            // 通過ContentResolver 向ContentProvider中查詢資料
            Cursor cursor2 = resolver2.query(uri, new String[]{"_id", "name","jobs"}, null, null, null);
            while (cursor2.moveToNext()) {
                // 將表中資料全部輸出
                this.userTv.append("    序號:" + cursor2.getInt(0) + "    姓名:" + cursor2.getString(1) +"    作業:"+cursor2.getString(2)+ "\n");
            }
            Toast.makeText(MainActivity.this,"插入成功",Toast.LENGTH_SHORT).show();
            // 關閉游標
            cursor2.close();

        }else {
            Toast.makeText(MainActivity.this,"請填寫完整，不能為空！",Toast.LENGTH_SHORT).show();
        }
    }

    private void btn_query2() {
        Uri uri  = Uri.parse("content://cn.sch.myprovider/user");

        Cursor query = getContentResolver().query(uri, null, null, null, null);
        //清空文本，防止重復查詢而多次顯示
        if(!TextUtils.isEmpty(this.userTv.getText()))
        {
            this.userTv.setText("");
        }
        while (query.moveToNext()) {
            int id = query.getInt(0);
            String name = query.getString(1);
            String job = query.getString(2);

            this.userTv.append("    序號:" + id + "    姓名:" + name +"    作業:"+job+ "\n");
        }
        query.close();
    }
}

MainActivity的activity_main.xml代碼如下

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:gravity="center"
        android:orientation="vertical">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginBottom="50dp"
            android:text="第二個應用"
            android:textSize="30dp" />

        <TextView
            android:id="@+id/id_tv"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginBottom="250dp"
            android:text="" />

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="2"
        android:gravity="center"
        android:orientation="vertical">


        <EditText
            android:id="@+id/xuhao2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:ems="10"
            android:hint="請輸入序號"
            android:inputType="number" />

        <EditText
            android:id="@+id/xingming2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:ems="10"
            android:hint="請輸入姓名"
            android:inputType="textPersonName" />

        <EditText
            android:id="@+id/zhiye2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:ems="10"
            android:hint="請輸入職業"
            android:inputType="textPersonName" />

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="2"
        android:orientation="vertical">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:gravity="center"
            android:orientation="horizontal">

            <Button
                android:id="@+id/btn_query2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="20dp"
                android:text="查詢資料" />

            <Button
                android:id="@+id/btn_insert2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginLeft="20dp"
                android:layout_marginTop="20dp"
                android:text="插入資料" />
        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:gravity="center_horizontal"
            android:orientation="horizontal">

            <Button
                android:id="@+id/btn_delete2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="洗掉資料" />

            <Button
                android:id="@+id/btn_update2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginLeft="20dp"
                android:text="更新資料" />
        </LinearLayout>
    </LinearLayout>

</LinearLayout>

第二個應用的AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="com.example.contentprovidertest">

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"
        tools:ignore="ProtectedPermissions" />
    <uses-permission android:name="android.permissions.READ_DATABASE"/>
    <uses-permission android:name="android.permissioms.WRITE_DATABASE"/>
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="cn.sch.myprovider.Read"/>
    <uses-permission android:name="cn.sch.myprovider.Write"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.MyApplication1">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

第二個應用的build.gradle

plugins {
    id 'com.android.application'
}

android {
    compileSdk 29

    defaultConfig {
        applicationId "com.example.contentprovidertest"
        minSdk 21
        targetSdk 29
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

dependencies {

    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'com.google.android.material:material:1.3.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
}

如果又遇到啥問題，可以留言，一起來解決，

到此所有代碼展示完畢，希望你們喜歡，覺得不錯的可以給我個贊哈，嘿嘿，